A high-frequency hot-melt copper-clad laminate and its preparation method

Abstract

This invention discloses a high-frequency hot-melt copper-clad laminate and its preparation method. The method includes steps such as coating with hot-melt resin, pre-stacking of multilayer boards, hot-press bonding, cold-press curing, and board separation, cutting, and post-processing. This invention uses modified hot-melt PI resin to replace the traditional PI layer and PP / pure adhesive layer, resulting in a thinner product structure that meets the requirements for lightweight electronic products. Simultaneously, by reducing the pure adhesive / PP lamination process, the multilayer board product processing technology is simplified. Different thicknesses can be produced by adjusting the thickness of the base film coating, simplifying manufacturing control. This invention, through process innovation, reduces costs, breaks with traditional production structures, and solves problems such as lamination blistering, hole residue, carbonization, and poor reliability that easily occur in multilayer flexible board lamination. The resulting copper-clad laminate possesses characteristics such as low dielectric constant, low high-frequency loss, high thermal conductivity, and low coefficient of thermal expansion.

Description

Technical Field

[0001] This invention belongs to the field of copper clad laminates, specifically relating to a high-frequency hot-melt copper clad laminate and its preparation method. Background Technology

[0002] Flexible copper clad laminate (FCCL) is an indispensable material in the electronics and electrical industry, and its quality and performance directly affect the stability and reliability of electronic devices. With continuous technological advancements, the application fields of FCCL are constantly expanding, and the requirements for its performance and quality are becoming increasingly stringent. Improving and perfecting its performance is of great significance for the high-frequency and high-speed development of electronic products. Compared to rigid FCCL, flexible FCCL has the advantages of being lightweight, small in size, and flexible, and has been widely used in both civilian and military technology products in recent years. Furthermore, flexible printed circuit boards (FPCs) made from flexible FCCL can significantly reduce the number of assembly steps, thereby reducing manufacturing costs and improving the reliability of final product assembly. It can also be used in applications requiring reduced gaps and lower weight.

[0003] Typically, FCCL (Flexible Clad Laminate) is a single-sided or double-sided flexible copper clad laminate composed of three layers: copper foil, adhesive, and base film. The base film is often polyester film or polyimide film; the adhesive is often epoxy resin or acrylic adhesive. There are also adhesive-free substrates, consisting of only two layers: copper foil and base film. When used in multilayer board production, it is also called a core board (CORE). Multilayer copper clad laminates are made by repeatedly laminating three or more core boards, pure adhesive / hot-melt PP, and a protective film (CVL). Metallized holes are formed through drilling and electroplating to connect the conductive layers, creating a multilayer board with a multi-layer conductor structure. Additionally, it requires design for localized delamination or removal of pure adhesive in bending areas to achieve high flexibility. However, during lamination, when adding pure adhesive / hot-melt PP layers to single-sided adhesive-free CCL, lamination bubbling or high-temperature lamination bubbling can easily occur, resulting in low product yield. This is especially true for the more layers and the thicker the product, the more problems arise. Furthermore, when creating through-holes, pure adhesive / PP is prone to carbonization, leading to stringing in the hole diameter. Additionally, PP is prone to puncturing the substrate after hardening. Simultaneously, with the development of high-frequency technology and the iterative updates of various high-frequency, high-speed copper-clad laminates, higher standards are required for flexible copper-clad laminates (FCCLs) used in circuit fabrication, placing higher demands on the quality and demand for upstream electronic resins. Specifically, in addition to excellent processability and mechanical properties, they must also possess a lower dielectric constant (Dk), low dielectric loss (Df) to minimize signal loss during transmission, and excellent thermal conductivity and coefficient of thermal expansion. Summary of the Invention

[0004] To address the shortcomings and deficiencies of existing copper-clad laminate (CCL) technologies, this invention provides a high-frequency hot-melt CCL and its preparation method. This method, through process innovation, reduces costs, breaks with traditional production structures, and improves production efficiency. Simultaneously, the resulting CCL possesses characteristics such as low dielectric constant, low high-frequency loss, high thermal conductivity, and low coefficient of thermal expansion.

[0005] This invention provides a method for preparing a high-frequency hot-melt copper-clad laminate, the method comprising the following steps:

[0006] (1) Coating with hot melt resin: hot melt PI resin is evenly coated on one side of copper foil, and then dried in an oven to obtain a single-sided core board.

[0007] (2) Multilayer board pre-stack: First, two single-sided core boards are aligned and stacked with the copper foil side facing out to form a double-sided core board. Then, at least one single-sided core board is placed on each side of the double-sided core board, with the copper foil side of the single-sided core board facing out to form a multilayer copper clad board.

[0008] (3) Hot pressing bonding: The multilayer copper-clad laminate is preheated and pressed to soften the hot melt PI resin and prepare for lamination; then, the multilayer copper-clad laminate is transported to the hot press for hot lamination. First, a vacuum is drawn to remove the air between the single-layer core boards, and then the hot press is heated to melt the hot melt PI resin, and then pressure is applied to press together; so that the hot melt PI resin forms a tight bond between the adjacent single-sided core boards.

[0009] (4) Cold pressing and curing: Maintain the pressing force and cool down to perform cold pressing. After cold pressing is completed, remove the multilayer copper-clad laminate from the hot press and cool and cure it.

[0010] (5) Board cutting and post-processing: According to the required size and shape, the multilayer copper-clad board after cooling and solidification is cut, and then the cut multilayer copper-clad board is trimmed, laser-drilled, and partially copper-plated in the through holes to obtain a multilayer high-frequency hot melt copper-clad board.

[0011] Preferably, the hot-melt PI resin is prepared by the following method:

[0012] S1. By weight, dissolve 10-20 parts of melamine and 20-50 parts of potassium hydroxide in dimethyl sulfoxide, stir until homogeneous, then add dropwise to dimethyl sulfoxide containing 10-20 parts of cyanuric chloride, and stir magnetically to mix the solution evenly; then add 100-150 parts of dopamine, and treat with ultrasonic vibration at 120-140℃ for 15-24 hours. After the reaction is completed, centrifuge, wash with dimethyl sulfoxide and pure water, and vacuum dry to obtain surface-modified COFs;

[0013] S2. By weight, add 3-5 parts of surface-modified COFs and 5-9 parts of cellulose nanofibers CNF to 150-200 parts of aprotic solvent. Under ultrasonic dispersion conditions of 20-30kHz, stir at a stirring speed of 1500-2000r / min for 2-4 hours to prepare a stable suspension.

[0014] S3. Add 75-95 parts of thermoplastic polyimide, 0.1-0.5 parts of ion scavenger, and 0.05-0.1 parts of antioxidant to the suspension and mix. Disperse the mixture using a high-speed disperser at a temperature of 40-50℃ for 1-2 hours and a speed of 800-1200 r / min to obtain hot-melt PI resin.

[0015] Preferably, in step (1), after the single-sided core board is made, a pre-designed circuit pattern is made on each single-sided core board.

[0016] Preferably, in step (1), the drying temperature in the drying tunnel is 170-190℃ and the drying time is 1.5-2h.

[0017] Preferably, in step (3), the preheating and pressing treatment is carried out at a temperature of 180-200℃, a pressure of 0.3-0.5MPa, and a time of 10-30min.

[0018] Preferably, in step (3), the temperature is controlled at 320-330℃ during hot lamination, and the pressure can be divided into four stages: initial pressure, second stage pressure, third stage pressure, and fourth stage pressure. The initial pressure is maintained at 0.5-1MPa for 20-30s, the second stage pressure is maintained at 3-5MPa for 30-50s, the third stage pressure is maintained at 6-10MPa for 100-150s, and the fourth stage pressure is maintained at 1.5-2MPa for 30-50s.

[0019] Preferably, the cold pressing temperature is 80-100℃ and the cold pressing time is 15-20s.

[0020] Preferably, the copper foil is an ultra-low profile copper foil, and the copper foil needs to be cleaned and treated before coating to remove the oxide layer and impurities on the surface.

[0021] Preferably, the aprotic solvent is N,N'-dimethylacetamide.

[0022] The present invention also provides a high-frequency hot-melt copper-clad laminate, which is prepared by the above method.

[0023] The beneficial effects of this invention are:

[0024] (1) This invention uses hot melt PI (i.e. modified thermoplastic PI) to replace the traditional PI layer and PP / pure glue layer, making the product structure thinner and meeting the requirements of thinner and lighter electronic products; at the same time, the process of pressing pure glue / PP is reduced, which also simplifies the processing technology of multilayer board products; products of different thicknesses can be pressed by adjusting the thickness of the coating base film, and the control during manufacturing is simple.

[0025] (2) The hot melt PI of the present invention can effectively solve the problems of lamination blistering, hole residue, carbonization, and poor reliability that are easy to occur when laminating multilayer flexible boards. The hot melt PI has better temperature resistance, thinner product, better bending resistance, and easier laser hole turning. The method of the present invention saves the production cycle of multilayer flexible boards and saves lamination time, which reduces production costs, improves production efficiency, and improves product yield.

[0026] (3) This invention introduces polydopamine-modified COFs into a polyimide-based film. Polydopamine has uniform coverage and good adhesion, and can form a coating layer on various material surfaces, enhancing the adhesion of the material surface. In addition, polydopamine has abundant surface functional groups, which can react with resin and COFs simultaneously to achieve material functionalization and modification, thereby avoiding the aggregation of COFs in the resin, which would lead to uneven dispersion. Covalent organic framework (COF) nanoparticles have a highly ordered and porous pore structure, which enables the PI-based film to obtain a low dielectric constant and low dielectric loss. In the PI matrix, the thermally conductive network with CNF as the main thermal conduction path and COFs dispersed in the structure as thermal conduction branches generates a relatively high thermal conductivity. Therefore, the synergistic modification of the PI material by the three can enhance the interlayer bonding force and reduce the dielectric constant and dielectric loss of the base film. In addition, the coefficient of thermal expansion (CTE) of the hot-melt PI-based film is similar to that of the ultra-low profile copper foil used, and the dimensional stability is high. The hot-melt PI of the present invention has low dielectric constant, low dielectric loss, high dimensional stability, high thermal conductivity, low water absorption and excellent mechanical properties, so as to meet the requirements of dielectric and loss parameters in practical applications and achieve better compliance with the needs of flexible boards for 5G high-frequency / high-speed transmission applications. Attached Figure Description

[0027] Figure 1 This is a process flow diagram of one embodiment of the present invention.

[0028] Figure 2 This is a schematic diagram of the structure of a single-sided core board in one embodiment of the present invention.

[0029] Figure 3 This is a schematic diagram of the structure of a four-layer copper-clad laminate in one embodiment of the present invention.

[0030] 1 is copper foil, 2 is hot-melt PI resin, 3 is double-sided core board, and 4 is single-sided core board. Detailed Implementation

[0031] The following specific examples illustrate the embodiments of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and various details in this specification can be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention.

[0032] Example 1

[0033] A method for preparing a high-frequency hot-melt copper-clad laminate includes the following steps:

[0034] (1) Coating hot melt resin: Hot melt PI resin is uniformly coated on one side of copper foil using a coating machine or roller coating machine. Ultra-low profile copper foil is selected. Before coating, the copper foil needs to be cleaned and treated to remove the oxide layer and impurities on the surface. Then, it is dried in an oven at a temperature of 180°C for 2 hours to obtain a single-sided core board to ensure the uniformity and consistency of the adhesive. Then, the pre-designed circuit pattern is made on each single-sided core board by sequentially applying photosensitive film, exposure, development, copper plating, and etching.

[0035] The hot-melt PI resin is prepared by the following method:

[0036] S1. By weight, 10 parts of melamine and 20 parts of potassium hydroxide were dissolved in dimethyl sulfoxide and stirred evenly. Then, 10 parts of cyanuric chloride were added dropwise to dimethyl sulfoxide and the solution was stirred magnetically to mix evenly. Then, 100 parts of dopamine were added and the mixture was ultrasonically vibrated at 120°C for 15 hours. After the reaction was completed, the mixture was centrifuged, washed with dimethyl sulfoxide and pure water, and vacuum dried to obtain surface-modified COFs.

[0037] S2. By weight, add 4 parts of surface-modified COFs and 7 parts of cellulose nanofiber CNF to 180 parts of aprotic solvent N,N'-dimethylacetamide (DMAc), and under ultrasonic dispersion at 25 kHz, stir at a stirring speed of 1800 r / min for 3 h to prepare a stable suspension.

[0038] S3. Add 85 parts of thermoplastic polyimide Mitsui Chemicals PL450C, 0.3 parts of ion capture agent IXE-100, and 0.08 parts of antioxidant L1010 to the suspension and mix. Disperse the mixture using a high-speed disperser at 45°C for 1.5 hours and a speed of 1000 r / min to obtain hot-melt PI resin.

[0039] (2) Multilayer board pre-stack: First, two single-sided core boards are aligned and stacked with the copper foil side facing out to form a double-sided core board. Then, a single-sided core board is placed on both sides of the double-sided core board, with the copper foil side of the single-sided core board facing out, to form a four-layer flexible board to be pressed.

[0040] (3) Hot-press bonding: The pre-stacked multilayer copper-clad laminate is preheated and pressed to soften the hot-melt PI and prepare for lamination. The preheating and pressing temperature is 180℃, the pressure is 0.3MPa, and the time is 10min. Then, the multilayer copper-clad laminate is transported to a hot press for hot lamination. First, a vacuum is drawn to remove the air between the single-layer core boards. Then, the hot press heats the hot-melt PI resin to melt and bond the adjacent single-sided core boards. Pressure is then applied to press the laminate together. The hot-melt PI resin is evenly distributed between the copper foils to form a tight bond between the adjacent single-sided core boards. The temperature is controlled at 320℃ during hot lamination, and the pressure can be divided into four... The process consists of four stages: initial pressure, second-stage pressure, third-stage pressure, and fourth-stage pressure. Initial pressure ensures tight bonding and heat transfer between each layer, expelling volatiles and residual gases. Second-stage pressure allows the molten fluid (residual adhesive, etc.) to smoothly fill and expel air bubbles within the adhesive, while preventing wrinkles and stress caused by excessive initial pressure. Third-stage pressure induces a polymerization reaction, causing the material to oxidize. Fourth-stage pressure maintains appropriate pressure during the cooling phase, reducing internal stress associated with cooling. The initial pressure is maintained at 0.5 MPa for 20 seconds, the second-stage pressure at 3 MPa for 30 seconds, the third-stage pressure at 6 MPa for 100 seconds, and the fourth-stage pressure at 1.5 MPa for 30 seconds.

[0041] (4) Cold pressing and curing: Maintain the pressing force and cool down to perform cold pressing. The cold pressing temperature is 80℃ and the cold pressing time is 15s. After the cold pressing is completed, the multilayer copper-clad laminate is taken out from the hot press and cooled and cured. During the cooling process, the hot melt PI resin gradually cures and forms a stable structure, so that the four single-sided core boards are firmly bonded together.

[0042] (5) Separation and post-processing: According to the required size and shape, the four-layer copper clad board is separated and cut. Then, the cut four-layer copper clad board is conveyed to the milling machine for edge trimming via a conveyor belt. Then, the trimmed four-layer copper clad board is laser drilled by an XRAY drilling machine. Finally, the four-layer copper clad board is copper plated on the whole board or partially copper plated in the through holes to obtain a four-layer high-frequency hot melt copper clad board.

[0043] Example 2

[0044] A method for preparing a high-frequency hot-melt copper-clad laminate includes the following steps:

[0045] (1) Coating hot melt resin: Hot melt PI resin is uniformly coated on one side of copper foil using a coating machine or roller coating machine. Ultra-low profile copper foil is selected. Before coating, the copper foil needs to be cleaned and treated to remove the oxide layer and impurities on the surface. Then, it is dried in an oven at a temperature of 190°C for 2 hours to obtain a single-sided core board to ensure the uniformity and consistency of the adhesive. Then, the pre-designed circuit pattern is made on each single-sided core board by sequentially applying photosensitive film, exposure, development, copper plating, and etching.

[0046] The hot-melt PI resin is prepared by the following method:

[0047] S1. By weight, 15 parts of melamine and 40 parts of potassium hydroxide were dissolved in dimethyl sulfoxide and stirred evenly. Then, 15 parts of cyanuric chloride were added dropwise to dimethyl sulfoxide and the solution was stirred magnetically to mix evenly. Then, 130 parts of dopamine were added and the mixture was ultrasonically vibrated at 130°C for 20 hours. After the reaction was completed, the mixture was centrifuged, washed with dimethyl sulfoxide and pure water, and vacuum dried to obtain surface-modified COFs.

[0048] S2. By weight, add 3 parts of surface-modified COFs and 6 parts of cellulose nanofiber CNF to 150 parts of aprotic solvent N,N'-dimethylacetamide (DMAc), and under ultrasonic dispersion at 25kHz, stir at a stirring speed of 1800r / min for 3 hours to prepare a stable suspension.

[0049] S3. Add 85 parts of powdered thermoplastic polyimide Mitsui Chemicals PL450C, 0.3 parts of ion capture agent IXE-100, and 0.08 parts of antioxidant L1010 to the suspension and mix. Disperse the mixture using a high-speed disperser at 45°C for 1.5 hours and 1000 r / min to obtain hot-melt PI resin.

[0050] (2) Multilayer board pre-stack: First, two single-sided core boards are aligned and stacked with the copper foil side facing out to form a double-sided core board. Then, a single-sided core board is placed on both sides of the double-sided core board, with the copper foil side of the single-sided core board facing out. After the required number of flexible boards are attached, a six-layer flexible board to be pressed is formed.

[0051] (3) Hot-press bonding: The pre-stacked multilayer copper-clad laminate is preheated and pressed to soften the hot-melt PI and prepare for lamination. The preheating and pressing temperature is 200℃, the pressure is 0.5MPa, and the time is 30min. Then, the multilayer copper-clad laminate is transported to a hot press for hot lamination. First, a vacuum is drawn to remove the air between the single-layer core boards. Then, the hot press heats the hot-melt PI resin to melt and bond the adjacent single-sided core boards. Pressure is then applied to press the laminate together. The hot-melt PI resin is evenly distributed between the copper foils, so that the adjacent single-sided core boards form a tight bond. The temperature is controlled at 330℃ during hot lamination, and the pressure can be adjusted. The process consists of four stages: initial pressure, second stage pressure, third stage pressure, and fourth stage pressure. Initial pressure ensures tight bonding and heat transfer between each layer, expelling volatiles and residual gases. Second stage pressure allows the molten fluid (residual adhesive, etc.) to smoothly fill and expel air bubbles within the adhesive, while preventing wrinkles and stress caused by excessive initial pressure. Third stage pressure induces a polymerization reaction, causing the material to undergo oxidation. Fourth stage pressure maintains appropriate pressure during the cooling phase to reduce internal stress associated with cooling. The initial pressure is maintained at 1 MPa for 30 seconds, the second stage at 5 MPa for 50 seconds, the third stage at 10 MPa for 150 seconds, and the fourth stage at 2 MPa for 50 seconds.

[0052] (4) Cold pressing and curing: Maintain the pressing force and cool down to perform cold pressing. The cold pressing temperature is 100℃ and the cold pressing time is 20s. After the cold pressing is completed, the multilayer copper-clad laminate is taken out from the hot press and cooled and cured. During the cooling process, the hot melt PI resin gradually cures and forms a stable structure, so that the six single-sided core boards are firmly bonded together.

[0053] (5) Separation and post-processing: According to the required size and shape, the six-layer copper clad board is separated and cut. The cut six-layer copper clad board is then conveyed to the milling machine for edge trimming via a conveyor belt. The trimmed six-layer copper clad board is then laser-drilled using an XRAY drilling machine. Finally, the six-layer copper clad board is copper-plated on the whole board or partially copper-plated in the through holes to obtain a high-frequency hot-melt copper clad board with a six-layer structure.

[0054] Comparative Example 1

[0055] A copper-clad laminate, the difference between this comparative example and Example 1 is that: in the hot-melt PI preparation process of this comparative example, steps S1 and S2 are omitted, and 5-10 parts of COF suspension are not added in S3, while other steps and conditions are the same as in Example 1.

[0056] Comparative Example 2

[0057] A copper-clad laminate, the difference between this comparative example and Example 1 is that: in the hot-melt PI preparation process of this comparative example, 100-150 parts of dopamine were not added in step S1, and the other steps and conditions were the same as in Example 1.

[0058] Comparative Example 3

[0059] A copper-clad laminate, the difference between this comparative example and Example 1 is that: in the preparation process of the copper-clad laminate in this comparative example, a commercially available thermoplastic PI product (Mitsui Chemicals PL450C, Japan) is used to replace the hot-melt PI resin, and the other steps and conditions are the same as in Example 1.

[0060] Comparative Example 4

[0061] A copper-clad laminate, the difference between this comparative example and Example 1 is that: in the hot-melt PI preparation process of this comparative example, cellulose nanofibers (CNF) were not added in step S2, while the other steps and conditions were the same as in Example 1.

[0062] Test case

[0063] The performance of the four-layer copper clad laminates prepared in Examples 1 and 2 and Comparative Examples 1-4 was tested.

[0064] Test method: The performance of the high-frequency hot-melt copper-clad laminates (single-sided core boards) prepared in the examples and comparative examples was tested using the industry-standard IPC-TM-650 test method. The test results are shown in Table 1.

[0065] Table 1 Performance Results of Copper-Clad Multilayer Copper-Clad Laminates

[0066] index Example 1 Example 2 Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 Dielectric constant (Dk) (10 GHz) 2.1 2.2 3.2 3.1 3 4 2.7 Dielectric loss (Df) (10 GHz) <![CDATA[1.4×10 -3 ]]> <![CDATA[1.5×10 -3 ]]> <![CDATA[3.9×10 -3 ]]> <![CDATA[2.9×10 -3 ]]> <![CDATA[4.5×10 -2 ]]> <![CDATA[2.4×10 -2 ]]> Peel strength (N / mm) 1.43 1.46 1.35 0.97 0.68 1.28 CTE (ppm / ℃) 19 20 30 27 40 34 Thermal conductivity (W / (mK)) 1.47 1.43 1.23 1.28 0.16 0.31

[0067] Summarizing the data in Table 1, it can be seen that Example 1 exhibits the best overall performance. This invention introduces polydopamine-modified COFs and cellulose nanofibers (CNFs) into a polyimide-based film. Polydopamine possesses uniform coverage and good adhesion, enabling it to form a coating layer on various material surfaces and enhancing surface adhesion. Furthermore, polydopamine is rich in surface functional groups, allowing it to react simultaneously with resins and COFs, achieving material functionalization and modification, thereby preventing COFs from agglomerating in the resin and causing uneven dispersion. Covalent organic framework (COF) nanoparticles possess a highly ordered, porous structure. The pore structure of COFs is one of their unique properties. By precisely controlling the building blocks and synthesis conditions, the pore structure of COFs can be finely controlled, resulting in a low dielectric constant and low dielectric loss in the PI-based film. In addition, the thermal conductivity of the polyimide film (0.16 W / m²) is... -1 K -1The scattering of phonons is relatively low, while the crystals present in cellulose nanofibers (CNFs) reduce phonon scattering. When cellulose nanofibers are arranged and connected in the form of filaments, the elongated structure forms a thermally conductive pathway, exhibiting strong thermal conductivity. Through specific preparation processes and material design, a thermally conductive network was formed in the PI matrix, with CNFs as the main thermally conductive pathway and COFs dispersed in the structure as thermally conductive branches, achieving a relatively high thermal conductivity (1.47 W / m²). -1 K -1 The synergistic modification of PI materials by these three agents can enhance interlayer bonding, reduce the dielectric constant and dielectric loss of the base film.

[0068] Furthermore, the known coefficient of thermal expansion (CTE) of copper is approximately 16 to 17 PPM / ℃, while the CTE of polyimide films is generally around 40 PPM / ℃. This invention introduces highly ordered, porous COF structures, abundant functional groups on the surface of polydopamine, and cross-linking structures into the polyimide molecular structure. These structures reduce molecular spatial hindrance, enhance interactions between molecular chains, restrict molecular chain movement, resulting in denser molecular chain packing and a smaller free volume, thereby lowering the coefficient of thermal expansion. Therefore, the CTE of the polyimide film developed in this invention is controlled below 25 PPM / ℃. This ensures that the CTE of the film is closer to that of copper during the manufacture of FCCLs, meeting the critical requirements for the performance and reliability of flexible copper-clad laminates (FCCLs), and thus avoiding device failures due to differences in thermal expansion.

[0069] Through the above examples and comparative comparisons, it was found that if PI is not modified and only commercially available thermoplastic PI is used, even with the most stringent pressing parameters, the interlayer adhesion of the flexible copper-clad laminate is poor, with high DK and DF values, failing to meet the application requirements of high-frequency copper-clad laminates. Adding COFs can reduce the DK and DF values ​​of the copper-clad laminate. Adding dopamine forms polydopamine-dispersed COFs, improving the electrical properties of the PI resin and enhancing interlayer adhesion. Furthermore, the study also found that low-content cellulose nanofibers (CNFs) showed good modification effects, but high-content CNFs performed poorly. This is because high-content CNFs agglomerate, failing to fully contact the PI molecular chains, and the large amount of agglomerated CNFs forms defects in the matrix, easily leading to stress concentration upon impact and causing cracks to initiate from these points, thus reducing the material's impact strength. Therefore, the specific manufacturing methods and performance of hot-melt copper clad laminates may vary depending on different production processes and material selections. Various raw materials need to be rationally combined to achieve synergistic effects, imparting excellent dielectric properties, thermal conductivity, coefficient of thermal expansion, and interlayer bonding strength to the copper clad laminate. Thus, strict control of process parameters is necessary during the manufacturing process to ensure the consistency and stability of product quality.

[0070] The embodiments described above are merely illustrative of several implementations of the present invention and are not intended to limit the scope of the invention. For those skilled in the art, any modifications, equivalent substitutions, or improvements made without departing from the concept of the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of this patent should be determined by the appended claims.

Claims

1. A method for preparing a high-frequency hot-dipped copper plate, characterized by, The preparation method comprises the following steps: (1) hot melt resin coating: uniformly coat hot melt PI resin on one side of a copper foil, then pass through an oven to dry, to obtain a single-sided core board; (2) multi-layer board pre-lamination: first align and laminate two single-sided core boards to form a double-sided core board, with the copper foil side outward, then place at least one single-sided core board on each side of the double-sided core board, with the copper foil side outward, to form a multi-layer copper-clad plate; (3) hot pressing and bonding: pre-heat press the multi-layer copper-clad plate to soften the hot melt PI resin and prepare for lamination; then, transport the multi-layer copper-clad plate to a hot press for hot lamination, first vacuumize to remove air between the single-layer core boards, then heat by the hot press to melt the hot melt PI resin, and then apply pressure to press and bond, so that the hot melt PI resin makes the adjacent single-sided core boards form a tight bond; (4) cold pressing and curing: maintain the pressing force and cool down for cold pressing, after cold pressing is completed, take out the multi-layer copper-clad plate from the hot press, and cool and cure; (5) board separation, cutting and post-processing: according to the required size and shape, cut the cooled and cured multi-layer copper-clad plate, and then carry out edge trimming, laser drilling and local copper plating in the through hole of the cut multi-layer copper-clad plate, to obtain a multi-layer structure high-frequency hot melt copper-clad plate; The hot melt PI resin is prepared by the following method: S1, according to the weight fraction, 10-20 parts of melamine, 20-50 parts of potassium hydroxide are dissolved in dimethyl sulfoxide, after stirring uniformly, 10-20 parts of cyanuric chloride are added dropwise in dimethyl sulfoxide, and the solution is uniformly mixed by magnetic stirring; then 100-150 parts of dopamine are added, ultrasonic oscillation treatment is carried out at 120-140℃ for 15-24h, after the reaction is completed, centrifugation, washing with dimethyl sulfoxide and pure water, vacuum drying, to obtain surface modified COFs; S2, according to the weight fraction, 3-5 parts of surface modified COFs and 5-9 parts of cellulose nanofiber CNF are added into 150-200 parts of aprotic solvent, under the condition of 20-30 kHz ultrasonic dispersion, stirring speed 1500-2000r / min, fully stirring for 2-4h, to prepare a stable suspension; S3, add 75-95 parts of thermoplastic polyimide, 0.1-0.5 parts of ion capture agent, 0.05-0.1 parts of antioxidant into the suspension, and mix, use a high-speed dispersion machine to disperse at a temperature of 40-50℃ for 1-2h, at a speed of 800-1200r / min, to obtain a hot melt PI resin.

2. The method of claim 1, wherein, In step (1), after the single-sided core board is prepared, a pre-designed circuit pattern is made on each single-sided core board.

3. The method of claim 1, wherein, In step (1), the temperature of the oven drying is 170-190℃, and the time is 1.5-2h.

4. The method of claim 1, wherein, In step (3), the pre-heat pressing temperature is 180-200℃, the pressure is 0.3-0.5MPa, and the time is 10-30min.

5. The method of claim 1, wherein, In the step (3), the temperature is controlled at 320-330 ℃ during the hot lamination, and the pressure can be divided into four stages: initial pressure, second-stage pressure, third-stage pressure, and fourth-stage pressure, the initial pressure is maintained at 0.5-1 MPa for 20-30 s, the second-stage pressure is maintained at 3-5 MPa for 30-50 s, the third-stage pressure is maintained at 6-10 MPa for 100-150 s, and the fourth-stage pressure is maintained at 1.5-2 MPa for 30-50 s.

6. The method of claim 1, wherein, The cold-pressing temperature is 80-100 ℃, and the cold-pressing time is 15-20 s.

7. The method of claim 1 wherein, The copper foil is an ultra-low profile copper foil, and the copper foil needs to be cleaned and treated before coating to remove the surface oxide layer and impurities.

8. The method of claim 1, wherein, The aprotic solvent is N, N'-dimethylacetamide.

9. A high frequency soldering copper clad plate, characterized by, Prepared by the method of any one of claims 1-8. Prepared by the method of any one of claims 1-8.

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